It has been customary for many years to use hop extracts instead of natural hops for brewing purposes. The use of extracts has a number of advantages, not only economic, but also with respect to brewing techniques and quality of product.
Several extraction procedures have been developed for extracting the resin portions and essential oils from the natural hop with organic solvents. Halogenated hydrocarbons such as methylene chloride, trichloroethylene and carbon tetrachloride as well as methanol, ethanol, acetone, n-hexane have been used singly and in various mixtures. These procedures extract primarily the essential oils resin portions, both hard and soft together with tannins and other substances; the relative quantities depending upon the polarity of the solvent.
Other procedures utilize mixtures of organic solvents with ammonia and water. Still others extract with water and use the aqueous solutions containing isomerization products for brewing purposes.
Frequently the resin portions are extracted with a first solvent, the spent hops then moistened to expel the first solvent and finally extracted with water. The solvent and water extracts are combined for use in brewing. Often the organic solvent extracts which are free from tannins are used alone in brewing. It has been observed that by this procedure the beers produced have good foam stability, while at the same time having low temperature stability and taste which differ little from beers produced with tannin containing extracts. (H. Schilfarth Mschr. Brauerei, 18, 65-77, 1965).
A persistent difficulty with presently known hop extracts is the removal of solvents from the extracts and from the spent hops. The syrupy or pasty masses which result from the usual extraction procedures release their solvent content only with great difficulty. Additionally, the chemical influence of the extraction solvents on the hop ingredients is not clear in many cases and may lead to the production of toxic components. These problems are very significant because of the requirement for the use of high purity components in brewing.
The invention is concerned with the production of hop extracts of high purity by a procedure which avoids the difficulties of previously known methods and may be utilized to produce tannin free, tannin containing and other specialized hop extracts.